1. Field of the Invention
The present invention relates to a magnetic recording medium. More particularly, the invention relates to an improvement of a magnetic recording medium comprising a nonmagnetic support and a magnetic recording layer.
2. Description of Prior Arts
A magnetic recording medium (hereinafter referred to sometimes as a magnetic tape) such as an audio tape, a video tape, or a recording medium employed in a computer system, basically comprises a nonmagnetic support and a magnetic recording layer provided on the support. The magnetic recording layer comprises a ferromagnetic metal oxide powder such as a needle crystalline powder of .gamma.-Fe.sub.2 O.sub.3 or Co-containing .gamma.-Fe.sub.2 O.sub.3. Recently, a demand for a higher density recording system has increased, and hence a magnetic tape using a ferromagnetic metal powder has been employed in place of the conventional oxide-type ferromagnetic powder. Particularly, in an 8 mm-width type video system which has been recently employed in practice, a tape width of a video tape used therefor is narrower as compared with conventional VHS type or .beta. type video tapes, so that much higher density recording is desired for the tape. The 8 mm type video tape generally employs the ferromagnetic metal powder.
The ferromagnetic metal powder is high in a coercive force (Hc) and a residual flux density (Br). For this reason, the ferromagnetic metal powder is suitable for the high density recording system. However, the ferromagnetic metal powder inherently has a low hardness, and therefore a magnetic recording medium employing said powder is poor in the running endurance (or running property). That is, in the magnetic recording medium using the ferromagnetic metal powder, a magnetic recording layer is liable to be damaged on its surface, or the ferromagnetic metal powder is apt to drop off from the magnetic recording layer. Particularly in the case of the video tape, the magnetic recording layer shows only a short still life in the still mode in which a still video image is continuously reproduced.
It is known that an abrasive (i.e., hard particles) such as corundum, silicon carbide or chromium oxide can be incorporated into the magnetic recording layer to improve the running endurance of the magnetic recording medium using the ferromagnetic metal powder. However, for obtaining prominent effect of incorporation of the abrasive, the abrasive is required to be contained in the magnetic recording layer in a large amount. The increase of an amount of the abrasive contained in the magnetic recording layer eventually brings about decrease of the amount of the ferromagnetic metal powder incorporatable in the same layer. In other words, in the art of a magnetic recording medium conventionally employed, a magnetic recording medium is unavoidably decreased in the electromagnetic conversion characteristics in exchange for the improvement of the running endurance.